Focal Segmental Glomerulosclerosis (FSGS) is a progressive disorder of the kidney of unknown etiology that results in proteinuria and End Stage Renal Disease (ESRD). Currently, we have limited insights into the molecular mechanism(s) underlying the development of segmental glomerulosclerosis. In the current application, we propose to determine the genetic defects underlying autosomal dominant forms of familial FSGS by applying positional cloning strategies. We have identified families in which FSGS is inherited as a Mendelian trait with high penetrance. To date, we have collected 50 multiplex, multi-generational families containing 219 affected individuals and banked DNA on 543 of these family members including 114 affected subjects. In preliminary studies, we established linkage to chromosome 11q21-22 and demonstrated that familial FSGS is genetically heterogeneous. We plan to take a systematic approach to study familial FSGS that includes: (1) expanding existing and collecting additional families with familial FSGS, (2) genome wide mapping of unlinked families to define the full spectrum of genetic heterogeneity, (3) narrowing the minimal candidate region (MCR) using recombinant and haplotype analysis, and (4) identifying the mutant FSGS gene. Initially, we will narrow the MCR on chromosome 11 where we have established linkage and later apply a similar paradigm to other FSGS loci. We have identified a YAC contig spanning the MCR on chromosome 11q21-22, which will be verified to provide a framework for mapping of Expressed Sequence Tag Sites (ESTs), microsatellites and genes in the region. Once this framework is established, a PAC/BAC contig will be constructed that will serve as a resource for generating new polymorphic markers and candidate genes to identify the FSGS defect. New candidate genes will be identified using direct selection from non-chimeric YACs or PACs. Candidate gene mapped to the MCR will be fully identified and screened for mutations in affected individuals. These investigations are critical to our understanding of the molecular basis of FFSGS. Knowledge derived from FFSGS will also allow a better understanding of pathogenesis of non-hereditary forms FSGS and may provide insights regarding management of the more common sporadic forms of this disorder.